It is well know that needle stick injuries by protruding needle cannula can result in innocent transmission of hepatitis B and AIDS (acquired immune disease syndrome). There have been several known cases of death resulting from accidental needle stick with contaminated needles. With the advent of the up to now incurable AIDS disease, there is an ever growing concern for a safer medical device to substantially reduce the possibility of hospital personnel being injured by the protruding needle during and after use. Also in order to prevent the spread of disease among drug abusers sharing the same syringes, a safer syringe against needle transmitted diseases is required.
There has been a lot of efforts in our hospitals to educate hospital personnel to take every possible caution to prevent needle stick injuries and to take appropriate medical treatments after needle-stick. However, a more fundamental solution to prevent the injuries as strongly recommended by senior medical professionals, is to develop a new syringe with improved structures which eliminate the operation procedures mostly responsible for the currently reported injuries cases. As a result, until the end of 1992, there have been over 50 U.S. patents disclosing various devices to prevent the sharp needle cannula from coming in contact with human skin. These devices generally fall into two catagories.
The first of the two catagories involved sheathing the needle cannula with an extra plastic tube slidable axially along the syringe barrel and which can be locked in the desired position to protect the sharp needle point from sticking whoever is using and disposing of the syringes, during or after use. The second category falls into a device for retracting the needle cannula into the syringe barrel after use in order to eliminate recapping the needle after an injection and to eliminate disposing of the protruding needles in the waste container. Representative examples with a device capable of retracting the needle and S the needle carrier into the barrel are U.S. patents to John E. Hall, U.S. Pat. No. 4,935,015; Walter W. Gloyer, U.S. Pat. No. 5,112,315 and No. 4,747,830; Michael L. Haining, U.S. Pat. Nos. 4,950,251 and 4,790,822 and 5,152,750; Dinesh L. Vadher, U.S. Pat. Nos. 4,988,339; Laurel A. Novacek, U.S. Pat. No. 5,030,209; Joseph W. Blake, U.S. Pat. No. 4,986,813; Edward D. Dysarz, U.S. Pat. Nos. 4,973,316 and 4,978,343; and Lynn E. Davis, U.S. Pat. No. 5,098,492. Other representative examples of being able to retract only the needle, without a needle carrier into the barrel, are U.S. patents to Christine M. Szuszkiewicz, U.S. Pat. No. 5,163,907; Michael J. Nusbaum, U.S. Pat. No. 5,088,986; James Deluccia, U.S. Pat. No. 4,675,005; Terry M. Haber, U.S. Pat. Nos. 4,770,655 and 4,804,370 and 4,813,426 and 4,820,275 and 4,826,484 and 4,935,014 and 4,909,794 and 4,908,022; Edward F. Allard, U.S. Pat. No. 4,838,869; Alan B. Ranford, U.S. Pat. No. 4,950,241; Dinesh L. Vadher, U.S. Pat. No. 4,946,446; Kristen A. Ridderheim, U.S. Pat. No. 4,955,870; James J. Lennox, U.S. Pat. No. 4,966,593; R. Kern McGary, U.S. Pat. No. 5,053,010; Richard A. Jaffe, U.S. Pat. No. 5,067,942; Deborah G. C. Stevenson-Michener, U.S. Pat. No. 5,066,281; Gerald R. Paxton, U.S. Pat. No. 511,404; Jonathan Weisslet, U.S. Pat. No. 5,046,508; Morris. J. Baskas, U.S. Pat. No. 4,955,870; Michael J. Botich, U.S. Pat. No. 4,994,034; Baldwin P. Jennings, U.S. Pat. No. 4,643,200; Irene Haller, U.S. Pat. No. 4,692,156; Laurel A. Novacek, U.S. Pat. Nos. 5,112,318 and 5,122,124.
Nevertheless, those patents having a device capable of retracting only the needle, without the carrier, such as those disclosed in U.S. Pat. Nos. 5,163,907, 5,088,986, 4,675,005 . . . , 5,112,318 and 5,122,124 have several drawbacks, which are either too complicated structure or having too many components to be made at competitive prices against the currently available syringes, or practically impossible to function properly, although seemingly applicable theoretically. For example, in order to inject the medication or fluid into the huamn tissue, the frictional force between the needle and the plastic embedding it must be large enough to ensure that the needle will not retract prematurally when puncturing the skin for injection prior to intended retraction after use. Since the contact area between the needle and the plastic embedding the needle is very small, from the mechamics points of view, the frictional coefficient between the needle and the plastic has to be very large which is very difficult since, in order to reduce the pain of puncture, a thin silicon film is already on the needle to reduce the frictional coefficient, and that is contradictory to the requirement of the design with retractable needle. Moreover, in the manufacturing processes, it is practically impossible to assemble the needle into the tiny hole of the plastic barrel without very precise instruments and extreme care, to prevent damage of the tip of the needle. The industries can hardly manufacture these syringes at competitive prices with mass production. Although others proposed a screw locking device, for example, James Deluccia, U.S. Pat. No. 4,675,005, however, it is practically very inconvenient for a big hand to rotate a tiny plunger several turns in order to retract the needle. In addition, screws on injection molded parts makes them slow in production and expensive.
Those patented designs with needle and carrier retracting into the barrel after use are free from the above mentioned drawbacks and are more likely to be accepted if the structure is simple and the cost is truely competitive. Edward D. Dysarz, U.S. Pat. Nos. 4,978,343 and 4,973,316 disclosed a design with a spring to assist retracting the needle into the barrel, which was a two piece structure connected in one supposedly by untrasonic welding. However, this structure required more intensives labor to assemble and thus higher costs and furthermore, it required extreme care and costly precision instruments to install the needle in place without damaging the needle tip. Walter W. Gloyer, U.S. Pat. Nos. 5,112,315 and 4,747,830 and Dinesh L. Vadher, U.S. Pat. No. 4,988,339 also disclosed syringes with retractable needle carrier. Nevertheless, the structures were still too complicated with redundant structural elements to be manufactured at very competitive prices. Alternative designs were proposed by Joseph W. Blake, U.S. Pat. No. 4,986,813, in which the needle cannula was screwed onto the base of the barrel. The processes of assembly requires that the needle have no protection cap on the needle tip to guard against tip damage. Despite the fact that the structures of the plunger and the barrel were very complicated and expensive to make, the retracted needle engaged on the plunger after retraction may still easily fall off due to vibration and might protrude out of the open end of the barrel and incidentally injure whoever touches it. Another patented design by Laurel A. Novacek, U.S. Pat. No. 5,030,208 disclosed a too complicated structure with redundant elements and hence higher costs. The needle engaged and retracted by the plunger could still fall off accidently with vibration. Lynn E. Davis, U.S. Pat. No. 5,098,402, proposed another syringe design with retractable needle. Regretfully, it involved too many little components making assembly processes tedious and time consuming. From the functional points of view, the requirement to rotate the tiny plunger with force in order to undo and retract the needle into the barrel is very inconvenient in practice. During this rotational processes, the fragile section on the plunger could be broken by shear force due to the resistance arising from the tight engagement between the needle and the barrel to prevent medication or fluid leakage. In this design, the needle after retraction can still fall off the carrier inside the barrel and moves freely and even comes out of the barrel to injure whoever touches it.
A further patent design as disclosed by Richard C. Terrill, U.S. Pat. No. 4,978,340 also has several disadvantages. The needle tip was not well protected with a cap when assembling the needle onto the barrel, and hence extreme caution is required. In addition to the fact that the structure is complicated, requiring expensive tooling, a more serious problem is that after the retraction of the needle into the barrel either the needle can easily fall off the needle carrier and move freely or the needle carrier can easily disengage itself from the plunger since there is no permanent engagement device between them. The needle could easily injure people. The problems associated with the patent by John E. Hall, U.S. Pat. No. 4,935,015 are similar to the above mentioned designs. The needle tip without a cap to protect from damage during assembly of the needle onto the barrel requires extreme caution and expensive precise instruments. Moreover, since the needle is tightly engaged with screws on the distal end of the barrel to prevent leakage of medication or fluid, in the process of retracting the needle into the barrel by twisting the plunger, the fragile section on the plunger could easily be broken and hence could not retract the needle. Even if the needle is successfully retracted into the barrel, the engagement device between the needle and the plunger is too weak to permanently secure the needle from falling off the plunger. Therefor, these is also a potential danger for needle stick injuries even after needle retraction.
Furthermore, since plastic materials are very notch sensitive, the ease to break the plunger depends upon the notch tip at the fragile section on the plunger. John E. Hall's design of the plunger has directional problems around the plunger. This means that if bending force is applied between the flanges along the plunger, several bendings may be required to break the plunger and these repeated bending may disengage the needle from the plunger momentarily. Screws existing inside the distal end of the barrel also results in slow production, expensive parts and shorter tooling life due to more serious tooling wear.
The inventions by Michael L. Haining, U.S. Pat. Nos. 4,790,822, 4,950,251 and 5,152,750 also have several drawbacks which keep these designs away from being a safer device. As a matter of fact, the manufacturer and the end user can hardly tolerate a safer device being more expensive than the currently available syringes Haining's design also required more component parts and hence was more expensive than the commercially available syringes. Yet, his design wasn't really safer since it didn't actually resolve all the problems. In his design, as the plunger is pushed to a stop but before it pushes further to engage with the needle carrier for retracting the needle into the barrel, the syringe is pulled out of the skin of the patient being injected, because this further push really hurts the patient. In the meantime, the dead space between the carrier and the plunger carrying significant amount of expensive residual medication or fluid is hence wasted. This could waste significant amounts of expensive medical resources, considering the number of syringes used every year. Furthermore, the notch on the plunger is a very poor design, from the mechanics points of view. In order to easily break the plunger, the notch tip has better be as sharp as possible and be sharp all around. Haining's design of the plunger made it difficult to break the plunger easily since stress concentration could not be effectively generated on the notch tip in any direction the plunger may be rotated. The result is that you will in some cases have to repeatedly break the plunger several times, which creates problems, in that during the repeated binding processes of the plunger, the needle on the carrier will be forced to heavily touch the inner wall of the barrel several times and that will loosen the needle from the carrier. It happens quite often that the needle will fall off the carrier and injure whoever touches it, because there is no way to guarantee that the needle will stay permanently together with the carrier inside the barrel no matter what happens and consequently this is not a really safe design. It is therefore the intention of the invention to come up with a new design of syringe with retractable needle, which is simple in structure using the same number of component parts as the currently available syringe, and which costs no more than the current syringes. Yet it has all the desired retractable function, without any foreseeable drawbacks as discussed above. This new design should be able to be produced and used without special care or caution and it requires no skillful workers and expensive instruments to assemble. The dead space carrying the residual medication or fluid should be no higher than the current type. Furthermore, the needle should not fall off the carrier to injure people by any chance no matter what happens. It is also the intention of the invention to develop a syringe with retractable needle substantially free from all the above mentioned disadvantages or other foreseeable drawbacks.